Digital artery blood pressure monitor

ABSTRACT

An example of a digital artery blood pressure monitor may include a tactile sensor array disposed on an inner surface of a cuff, the tactile sensor array including a plurality of capacitive sensors to detect pressure changes within a digital artery of a finger due to blood flow, where the pressure changes cause changes to capacitance values of one or more capacitive sensors of the tactile sensor array, and control circuitry coupled to the tactile sensor array to receive the capacitance values from the tactile sensor array, and determine a blood pressure based on the capacitance values.

CROSS-REFERENCE TO RELATED APPLICATION

The present application is a divisional of U.S. application Ser. No.15/414,354, filed on Jan. 24, 2017, the contents of which are herebyincorporated by reference.

TECHNICAL FIELD

This disclosure relates generally to blood pressure monitoring, and inparticular but not exclusively, relates to blood pressure monitoring ata digital artery.

BACKGROUND INFORMATION

High blood pressure is a health concern for a large percentage of thepopulation, but regular monitoring is not common place. Blood pressuremonitors have conventionally been mainly used at a physician's office,hospital, and/or the occasional automated system found in pharmacies,but are not frequently used by those who suffer high blood pressureoutside of the occasional office visit or while waiting for aprescription at the pharmacy. Additional monitoring of blood pressure isrequested by many physicians, but patients rarely follow through due todifficulty in obtaining readings, expense of portable units, or theyavoid the readings due to the associated discomfort. The associateddiscomfort typically due to the squeezing of the arm or wrist, forexample. As such, it may be desirable to have portable, easy to use, andless painful blood pressure monitoring devices.

BRIEF DESCRIPTION OF THE DRAWINGS

Non-limiting and non-exhaustive embodiments of the invention aredescribed with reference to the following figures, wherein likereference numerals refer to like parts throughout the various viewsunless otherwise specified. Not all instances of an element arenecessarily labeled so as not to clutter the drawings where appropriate.The drawings are not necessarily to scale, emphasis instead being placedupon illustrating the principles being described.

FIG. 1A is a blood pressure monitoring device 100 in accordance with anembodiment of the present disclosure.

FIG. 1B is a perspective view of the finger wearable blood pressuremonitoring device 100 in accordance with an embodiment of the presentdisclosure.

FIG. 2 is a finger wearable blood pressure monitoring device 200 inaccordance with an embodiment of the present disclosure.

FIG. 3 is a finger-based blood pressure monitoring device 400 inaccordance with an embodiment of the present disclosure.

FIG. 4 is a functional block diagram of a finger-wearable BP monitoringdevice 400 in accordance with an embodiment of the present disclosure.

FIG. 5 is a plan view of a tactile sensor array 510 in accordance withan embodiment of the present disclosure.

FIGS. 6A and 6B are a cross-sectional view and a plan view,respectively, of a tactile sensor array (TSA) 610 in accordance with anembodiment of the present disclosure.

FIGS. 7A and 7B are a cross-sectional view and a plan view,respectively, of a TSA 710 in accordance with an embodiment of thepresent disclosure.

FIG. 8 is a bladder 806 in accordance with an embodiment of the presentdisclosure.

FIG. 9 is a bladder 906 in accordance with an embodiment of the presentdisclosure.

FIG. 10 is a bladder 1006 in accordance with an embodiment of thepresent disclosure.

FIG. 11 is an example pressure plot 1100 in accordance with anembodiment of the present disclosure.

FIG. 12 is a method 1200 in accordance with an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

Embodiments of a system and method for measuring blood pressure at adigital artery are described herein. In the following descriptionnumerous specific details are set forth to provide a thoroughunderstanding of the embodiments. One skilled in the relevant art willrecognize, however, that the techniques described herein can bepracticed without one or more of the specific details, or with othermethods, components, materials, etc. In other instances, well-knownstructures, materials, or operations are not shown or described indetail to avoid obscuring certain aspects.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure, orcharacteristic described in connection with the embodiment is includedin at least one embodiment of the present invention. Thus, theappearances of the phrases “in one embodiment” or “in an embodiment” invarious places throughout this specification are not necessarily allreferring to the same embodiment. Furthermore, the particular features,structures, or characteristics may be combined in any suitable manner inone or more embodiments.

Hypertension, e.g., high blood pressure, may affect large numbers of thepopulation, but the extent may be uncertain due to gaps in bloodpressure data. For example, outside of individuals who see a physicianregularly for various health concerns, most adults may only have theirblood pressure read once, maybe twice, a year. Further, variability inblood pressure over time or throughout the day may be a diagnosticindicator of other ailments that may not be apparent to the individual.As such, more blood pressure readings at various times of the day andyear may be desirable to help physicians better understand theirpatient's holistic health.

Although there are blood pressure monitoring stations at somepharmacies, and blood pressure monitoring devices available forpurchase, adoption of these means and devices may be lacking. The lackof adoption may be due to costs of the devices or unwanted trips to thepharmacy. However, even those individuals who do some self bloodpressure monitoring may take readings less often than desirable becausethe methods/devices are either cumbersome to operate, painful, or acombination thereof. Additionally, the data individuals may obtain ontheir own likely never gets communicated to their physician. Moreover,monitoring of blood pressure by individuals may be undesirable forseveral additional reasons, such as complacency by the individuals, thepain associated with the blood pressure monitoring, lack oftransportation, etc.

As such, it may be desirable to have a portable, compact device that mayless intrusively monitor a user's blood pressure. It may be furtherdesirable for the device to be small, simple to operate, and be capableof reporting blood pressure readings to a physician or a patient'selectronic medical records.

One way to provide for blood pressure monitoring may be afinger-wearable device that monitors blood pressure in a digital artery,such as the digital artery on the ulnar or radial sides for example. Thefinger-wearable device may use oscillometry, auscultation, orapplanation tonometry to estimate a user's blood pressure at the digitalartery, which may subsequently be converted to a clinical or brachialblood pressure. For applanation tonometry, the finger-wearable devicemay include a tactile sensor array that may be pressed into the fingerover the digital artery, which may deform to digital artery. The digitalartery may or may not be deformed to occlusion. As the pressure of thefinger onto the tactile sensor array is slowly reduced, the digitalartery may slowly convert back to a normal shape, and may pass through apoint where the internal pressure equals the external pressure exertedon the digital artery by the TSA. This point may occur when a localradius of the digital artery approaches infinity, e.g., zero, at leastin reference to a size of a capacitive sensor of the tactile sensorarray. In this state, e.g., with the local radius of curvature of thedigital artery flat, the blood flow in the artery due to heart beats maycause the flat area of the digital artery to experience fluctuations. Amaximum fluctuation may occur at the flat condition, andincreases/decreases of the fluctuations may occur when the local radiusis not quite flat. While the above operation was discussed in terms of acontrolled reduction in pressure between the finger and the tactilesensor array, the operation may alternatively be performed using acontrolled increase in pressure and the capacitance changes may bemeasured during the controlled increase.

The tactile sensor array may include deformable capacitive sensors thatmay be deformed due to the fluctuations in the arterial wall. Thesefluctuations may change a shape, e.g., height, of one or more deformablecapacitive sensors, which may change their capacitance values. Thechanging capacitance may be measured, which provides an indication ofthe blood pressure in the digital artery. The capacitance levels of thecapacitive sensors may be converted into pressure levels, e.g., mmHg. Amaximum amplitude of the capacitance fluctuations/changes may be anestimate of a mean arterial pressure at the digital artery. Then, asystolic and a diastolic blood pressure at the digital artery may beestimated based on the mean arterial pressure. Subsequently, the digitalartery blood pressure estimates may be converted to clinical or brachialblood pressure measurements.

To implement auscultation, the digital artery may be pressed toocclusion by the finger-wearable device then the pressure slowlyreduced. A microphone included in the device may record sounds, known asKorotkoff sounds, originating in the digital artery as the blood beginsto flow. The Korotkoff sounds change in character as the pressureapplied to the artery is decreased . The applied pressure correspondingto the first Korotkoff sound may be an estimate of the systolic bloodpressure, and the applied pressure corresponding to the termination ofthe Korotkoff sounds may be an estimate of the diastolic blood pressure.

To implement oscillometry, the digital artery may be pressed or squeezedby a bladder to a pressure at least above the systolic blood pressure,then the pressure may be slowly reduced. During the reduction inpressure, an air pressure sensor measuring the pressure in the bladdermay also measure pressure oscillations in the bladder due to blood flowin the digital artery. The pressure oscillations may start small,increase to a maximum amplitude, and reduce. Similar to the applanationtonometry technique, the applied pressure at maximum amplitude may be anestimate of the mean arterial pressure. From the mean arterial pressure,a systolic and diastolic pressure may be estimated.

FIG. 1A is a blood pressure monitoring device 100 in accordance with anembodiment of the present disclosure. The blood pressure monitoringdevice 100, device 100 for short, may be worn or engaged with a digitalartery, e.g., a finger, to determine the blood pressure of a user, alongwith other diagnostic data. In some embodiments, the other diagnosticdata may include heart rate (HR), respiratory rate (RR), temperature,and blood oxygen saturation (SpO2). In some embodiments, motion of thedevice 100 may also be detected. The device 100 may be worn on a fingerof a user throughout the day, night, both, or periodically to monitorthe user's blood pressure. In some embodiments, the device 100 mayprovide blood pressure readings, and the other diagnostic data/movementdata to an external reader (not shown). In turn, the external reader mayrecord the data, alert the user and/or user's physician to readingsoutside of designated ranges, or transmit the data to an electronicmedical record associated with the user, for example.

The illustrated embodiment of the device 100 includes a cuff 102, a sizeadjustment mechanism 104, a bladder 106, a substrate 108, a tactilesensor array (TSA) 110, control circuitry 112, and an alignment tab 114.The device 100 may be worn on a finger with the TSA 110 oriented toalign with a digital artery of the finger. In some embodiments, the TSA110 may be aligned 45° to the palm so that the TSA 110 is centered overthe digital artery on the ulnar side of the finger. The size adjustmentmechanism 104 may be adjusted to ensure a snug fit around the finger. Insome embodiments, the bladder 106 may be dynamically inflated to ensurethat the digital artery and the TSA 110 are pressed together.Subsequently, the TSA 110 may measure blood pulses in the digitalartery, which may be converted into mean arterial pressure (MAP),systolic blood pressure (SBP), and/or diastolic blood pressure (DBP). Insome embodiments, the control circuitry 112 may perform the conversion.In other embodiments, the measurements may be transmitted, via wire orwirelessly, to an external reader for the conversion process. While thedevice 100 includes the bladder 106 to facilitate pressure of the fingerto the TSA 110, in other embodiments, the bladder may be omitted and thesize adjustment mechanism 104 may be adjusted to provide the necessarypressure.

The cuff 102 may be formed to fit at least partially around a finger andmay further provide support for the various other components. The cuff102 may be formed from plastic, metal, ceramic, or any biocompatiblematerial not likely to affect the BP monitoring components/measurements.The cuff 102 may be ring-shaped with a radial thickness, a width (alongthe finger), and a circumference/diameter. The radial thickness may bethick enough to provide non-deformable support to the bladder 106 andTSA 110. The circumference may range from 22 to 25 mm, but may also beadjustable by the size adjustment mechanism 104 to fit a wide range offinger sizes. For example, the cuff 102 may be adjustable to fit aroundan index finger or a pinky finger. In some embodiments, the width andcircumference of the cuff 102, especially an inner surface of the cuff102, may be based on guidelines set by the AHA (American HeartAssociation) regarding inflatable cuff dimensions with respect to an armcircumference. Per the guidelines, the bladder 106 should have a lengththat is 80% and a width that is 40% of an arm circumference, whichresults in a length-width ratio of 2:1. As such, the inner circumferenceof the cuff 102 may desirably be large enough to allow the circumferenceand width of the bladder 106 to satisfy the ratio in regards to a fingercircumference.

The size adjustment mechanism 104 may be incorporated into a portion ofthe cuff 102, and may allow a user to adjust the size, e.g.,circumference, of the cuff 102 to obtain a desired fit. In someembodiments, the desired fit may be a snug fit that allows the fingerand the TSA 110 to be in intimate contact. It may be desirable toprevent a loose fit of the device 100 on the finger. However, the device100 may operate as intended even when loosely worn on a finger due tothe bladder 106 pressing the finger against the TSA 110. In someembodiments, the size adjustment mechanism 104 may be a ratcheting-typeadjustment as shown in FIG. 1. In other embodiments, the size adjustmentmechanism 104 may be formed from hook and loop, buckle, etc. types ofmechanisms. Of course, the size adjustment mechanism 104 may be omittedand the cuff 102 may be fitted or may be available in various sizesdepending on the user's fingers.

The bladder 106 may be disposed on an inner surface of the cuff 102 and,in some embodiments, may be disposed along a majority of the innercircumference of the cuff 102. In some embodiments, the bladder 106 maygenerally be disposed on an inner surface opposite from the location ofthe TSA 110. The bladder 106 may be formed from a soft, flexiblematerial that may enlarge/stretch due to an increase in internalpressure. In some embodiments, air may be introduced, e.g., pumped, inthe bladder 106 to cause the bladder 106 to expand. In otherembodiments, a refrigerant coupled to or disposed within the bladder 106may undergo a phase transition from liquid to gas to provide the desiredexpansion, with the phase transition induced through heating therefrigerant. Alternatively, the bladder 106 may be replaced by a shapememory alloy that may press the finger into the TSA 110 in response to acontrol voltage, for example, or a mechanical actuator may be used topress the finger onto the TSA 110. Although not shown in FIG. 1, apressure sensor may be disposed within the bladder 106 to measure theinternal pressure of the bladder 106. In some embodiments, the pressuresensor may be used to implement oscillometric estimates of the bloodpressure. Expansion of the bladder 106 may force a user's finger to bepressed more tightly against the TSA 110, which may provide betterinteraction between the TSA 110 and the digital artery aligned with theTSA 110.

The substrate 108 may provide a mounting surface for the TSA 110 and/orthe control circuitry 112. The substrate may be formed from a rigidmaterial, such as plastic, ceramic, or metal, and may be disposed on theinner surface of the cuff 102.

The TSA 110 may be a sensor array formed from a plurality of individualcapacitive sensors. The TSA 110 may be disposed on the substrate 108 andarranged to be in contact with the finger of the user. The plurality ofcapacitive sensors may be arranged into a two-dimensional arraycomprising a number of columns and a number of rows. In someembodiments, the columns may be arranged to align longitudinally withthe finger and the rows align circumferentially. Of course, the oppositearrangement of the columns and rows may be implemented. In someembodiments, there may be more columns than rows to ensure the TSA 110,or at least a column of capacitive sensors, is centered over the digitalartery area of the finger. In general, it may be desirable to have atleast one capacitive sensor of the TSA 110 to contact the skin directlyabove the digital artery so that pressure changed in the digital arterymay be measured as changes in capacitance of the at least one capacitivesensor. Additionally, the TSA 110 may be formed from a soft, flexiblematerial that conforms the inside shape of the cuff 102 and/or fits atleast partially around the finger. Alternatively, the TSA 110 may have asemi-circumferential shape to at least conform to an outside of thefinger.

In some embodiments, the TSA 110 may include a Kapton or Polyimidecapsulant layer on the finger side of the TSA 100. The Kapton orPolyimide layer may provide a mechanical, protective layer to the TSA110. In some embodiments, however, the Kapton or Polyimide layer may beseparated between the rows, columns, or individual capacitive sensors tomechanically decouple adjacent rows, columns, or individual capacitivesensors. In other embodiments, the TSA 110 may include a conductivecloth layer that provides an electrode to the individual capacitivesensors. The conductive cloth may mechanically decouple adjacentcapacitive sensors of the TSA 110. In general, the TSA 110 may becoupled to detect and measure blood flow in the digital artery due toheart beats, and the resulting blood pressure. For example, one or moreindividual capacitive sensors of the TSA 110 may be aligned with thedigital artery and may detect changes pressure changes within thedigital artery due to the capacitive sensor deforming in response topressure changes within the digital artery, which indicate blood flowand blood pressure. The detected changes in pressure, which cause achange in the capacitance reading of the TSA 110, may be converted intoMAP at the digital artery, which may subsequently be converted into SBPand DBP at the digital artery.

The control circuitry 112 may be coupled to choreograph the operation ofthe device 100, and may be disposed between the inner surface of thecuff 102 and the substrate 108. In some embodiments, the controlcircuitry 112 may be disposed on a side of the substrate 108 facing theinner surface of the cuff 102. In other embodiments, the controlcircuitry 112 may be disposed on the inner surface of the cuff 102underneath the substrate 108. The control circuitry 112 may be coupledto the TSA 110 to receive capacitance readings, and may be furthercoupled to the bladder 108 to control inflating and deflating.Additionally, the control circuitry 112 may be coupled via a wire orwirelessly to an external reader for providing and receiving data and/orpower.

The alignment tab 114 may assist the user in aligning the TSA 110 to adesired digital artery. For example, the alignment tab 114 may bealigned with the palm so that the TSA 110 may be aligned with thedigital artery. In some embodiments, the TSA 110 may be aligned with thedigital artery on the ulnar side of the finger, and the alignment may befacilitated by the alignment tab 114. While the digital artery on theradial side of the index finger may also be used to monitor BP, thedigital artery on the ulnar side may be more desirable due to it beinglarger and closer to the skin surface than the digital artery on theradial side. It is also possible to measure the BP from other fingers,including the long finger, ring finger and little finger.

FIG. 1B is a perspective view of the finger wearable blood pressuremonitoring device 100 in accordance with an embodiment of the presentdisclosure. FIG. 1B shows the TSA 110 disposed on the substrate 108,which is disposed on an inner surface 116 of the cuff 102. An electricalconnection 118 may be coupled to the control electronics 112 (notshown), which may be disposed beneath the substrate 108. Additionally,the alignment tab 104 is shown to be a long extension coupled to thecuff 102. The long extension may be slid into or positioned in/on thepalm of a user when a user puts the device 100 on a finger. In the shownorientation of the TSA 110 to the alignment tab 104, the device 100 maybe worn on a left hand so that the TSA 110 is aligned with the digitalartery on the ulnar side, for example. Although the alignment tab 104 isshown to be extending form the cuff 102, in other embodiments, alignmentmay be assisted from markings placed on the cuff 102.

In operation, the device 100 may detect and monitor the user's BP, alongwith the various other diagnostic variables. In some embodiments, thedevice 100 may implement applanation tonometry to determine the user BPat the digital artery, which may then be transformed into a brachial BPmeasurement. In other embodiments, the device 100 may implementoscillometry and/or auscultation to monitor the BP in the digitalartery. In general, the bladder 106 may be inflated to cause the fingerto press onto the TSA 110, then the bladder 106 may be deflated. Duringeither the inflation or the deflation of the bladder 106, the TSA 110may measure pressure pulses in the digital artery that may be convertedinto blood pressure estimations. For example, the bladder 106 may beinflated in a slow, controlled manner, and the pressure pulses may bemeasured when the TSA 110 is being slowly pressed into the digitalartery. Alternatively or additionally, the pressure pulses may bemeasured during a slow, controlled deflation of the bladder 106, whichmay allow the TSA 110 to slowly decrease pressure applied to the digitalartery. In either operation, the TSA 110 may create a condition on thearterial wall of the digital artery that allows applanation tonometry tobe performed, e.g., when a local radius of curvature of the digitalartery approaches infinity, at least compared to a size of a capacitivesensor of the TSA 110. While the detailed operation of the device 100may be described in terms of deflation of the bladder 106, the sameprinciples of operation may be applied during a slow, controlledinflation of the bladder 106.

To determine the BP using applanation tonometry, such as a MAP that canbe used to determine SBP and DBP, the control circuitry 112 may causethe bladder 106 to inflate to a pressure that is at least above the SBPof the user. In some embodiments, the bladder 106 may be inflated untilocclusion of the digital artery. Inflating to occlusion, however, maynot be necessary, but may be performed when the device 100 is initiallyused to ensure the pressure is above SBP. To determine if occlusion isreached, the TSA 110 may monitor for pressure changes via capacitancemeasurements. Once the bladder 106 has been inflated to the desiredpressure, the control circuitry 112 may deflate the bladder 106 at aslow and controlled rate. For example, the bladder 106 may be deflate ata rate of 2 to 3 mmHg per second. While the bladder is deflating, theTSA 110 may measure pressure changes occurring within the digital arterydue to the BP and blood flow. As the pressure exerted by the bladder 106decreases, the external pressure on the digital artery will decrease.The decrease in the external pressure on the digital artery affects thedifferential between the external pressure on the artery and theinternal pressure on the artery. As these two pressures tend towardbeing equal, at which time the arterial wall may be flat at least inregards to the capacitive sensor of the TSA 110, the blood flow pulsesdue to the heart beat begin to show a change as detected by the TSA 110.The changes may appear as pulsatile waveforms or fluctuations in thecapacitive measurements/levels of the TSA 110. The pressure at which amaximum amplitude occurs in a pulsatile waveform may be the MAP (meanarterial pressure), which may be indicative of the user's BP in thedigital artery. After detection of MAP, the control circuitry 112 mayprovide the data to an external reader for algorithmic manipulation toextract SBP and DBP from the MAP, or the control circuitry 112 mayestimate the MAP, SBP and DBP.

In response to the determination of MAP, SBP and/or DBP, the device 100may perform various tasks. For example, if the BP data show a high BPreading, the user may be alerted via the external reader to consulttheir physician or remind the user to take their BP medication.Alternatively, the data may be provided by the device 100 to be loggedon the external reader, which may periodically upload the data to theuser's electronic medical records, or to an application, for example. Insome embodiments, the external reader may provide distractions to theuser while a BP reading is performed. For example, the external reader,which may be a smartphone, may provide news, weather, games, or heartbeat waveforms while a BP reading is performed.

While the device 100 may be a ring-type device to be freely worn on afinger, the device 100 may be included in various other wearable orhandheld devices as well. For example, the device 100 may be insertedinto a finger of a glove to be worn by the user, or the device 100 maybe included in a handheld device that may include a display and otherindicators to assist the user with operation.

FIG. 2 is a finger wearable blood pressure monitoring device 200 inaccordance with an embodiment of the present disclosure. The fingerwearable blood pressure monitoring device 200, device 200 for short, maybe an example of the device 100. The device 200 may be formed to fit, atleast partially, around a finger to monitor for blood pressure and otherdiagnostic data using a digital artery. For example, the device 200 maydetect a digital artery-based BP using one or more capacitive sensors,and augment the BP data with heart rate, respiratory rate, temperature,sound, and movement data. The other diagnostic data may provideinformation to a user or physician on their own, but may also be used toinform the BP measurement. In general, the device 200 may determine aMAP at the digital artery, which may then be algorithmically convertedinto SBP and DBP at the digital artery. Additionally, the digital arteryBP data may be converted to clinical/brachial BP data through one ormore transfer functions. In some embodiments, estimation of the BP atthe digital artery and/or the conversion to the clinical/brachial BP maybe performed by control logic included in the device 200. In otherembodiments, the control circuitry may provide the raw capacitance dataalong with other sensor data to an external device for analysis andreporting of the data and BP estimation.

The illustrated embodiment of the device 200 includes a cuff 202, a sizeadjustment mechanism 204, a bladder 206, a substrate 208, TSA 210,control circuitry 212, accelerometer 220, temperature sensor 222,photoplethysmography (PPG) sensor 224, and a microphone 226. The cuff202, size adjustment mechanism 204, bladder 206, substrate 208, and TSA210 may be analogous to like components of the device 100, and, as such,a detailed discussion with respect to FIG. 2 is omitted for sake ofbrevity.

The accelerometer 220 may measure movement of the finger and provide themeasurements to the control circuitry 212. The accelerometer 220 may bedisposed on the cuff 202, such as an inner surface of the cuff, or maybe imbedded into the cuff 202. Movement of the finger during a BPmeasurement may affect the accuracy of the measurement. However, withknowledge of the intensity of the movement, the control circuitry 212may ignore the movement and continue the reading, halt the reading,adjust the reading based on the movement, or reject the BP reading.Additionally, the accelerometer may be used to reduce hydrostaticeffects of the BP reading that occur when the finger is at a differentelevation/height than the heart. For example, the accelerometer maymeasure movement and orientation of the device 200 before a BP readingif the user is prompted to move the finger level with their heart.

The temperature sensor 222 may be disposed on the inner surface of thecuff 202 and be arranged to be in intimate contact with the finger atleast during a BP reading. The temperature sensor 222 may measure atemperature of the finger, such as skin temperature, and provide themeasurement to the control circuitry 212. The temperature measurementmay be used to adjust for vasomotor effects in the digital arteries.Because digital arteries are more susceptible to vasoconstriction andvasodilation, which may alter the peripheral blood flow and BPmeasurements, the temperature of the finger may be used to compensatethe BP measurement if the temperature is outside of a set range. Forexample, if the temperature is less than 25 Celsius or greater than 40Celsius, the BP estimation may be adjusted. For example, if the fingertemperature is low, the device may request the user to warm the handsand repeat a measurement. Alternatively, the device may use the changesin compliance of the digital artery at different temperatures to correctthe raw BP estimates.

The PPG sensor 224 may be disposed on the inner surface of the cuff 202and be arranged to emit light through the finger and detect the light asit propagates out of the finger. The PPG sensor 224 may include redand/or infrared emitters and respective receivers/detectors, forexample. The red and infrared emitters may be light emitting diodes(LEDs) and the receivers, which may be tuned to red and infraredwavelengths, may be photodetectors. The PPG sensor 224 may be used todetect heart rate (HR), respiratory rate (RR), and blood oxygensaturation (SpO2) of the user based on absorption of the red andinfrared light. Additionally, the PPG sensors 224 may be used to detecttiming of the pulses occurring in the digital artery. The timinginformation may be used to inform when to begin and/or to end the BPmeasurements, for example. The light absorption data determined by thePPG sensor 224 may be provided to the control circuitry 212, which maythen determine the HR, RR and SpO2 based thereon.

The microphone 226 may also be disposed on the inner surface of the cuff202, and be coupled to record the blood pulses occurring in the digitalartery. In some embodiments, the microphone 226 may be a piezoelectricmicrophone. The sound recordings, which may be provided to the controlcircuitry 212, may be used to detect Korotkoff sounds for blood pressureestimation. The Korotkoff sounds may be used to implement auscultatorytechniques.

The control circuitry 212 is coupled to the various sensors andelectronic components of the device 200, and choreographs the operationof the device. The control circuitry 212 may include ananalog-to-digital converter (ADC) coupled to receive the analog signalsfrom the various sensors and convert the same into digitalrepresentations. The digital representations may then be used by thecontrol circuitry 212 to determine the user's digital BP and provide theHR, RR and SpO2 as well. Else, the control circuitry 212 may provide thedigital representations via a wired or wireless connection to anexternal reader for determination of the digital artery BP. In someembodiments, the control circuitry 212 may receive capacitancemeasurements from the TSA 210, which may then be used to determine theMAP, and in turn the SBP and DBP of the user. Else, the capacitivemeasurements may be provided to the external reader for estimation ofthe MAP, SBP and DBP.

FIG. 3 is a finger-based blood pressure monitoring device 300 inaccordance with an embodiment of the present disclosure. Thefinger-based blood pressure monitoring device 300, device 300 for short,may be an example implementation of the device 100 and/or 200. Thedevice 300 may be mounted to a stationary surface, contained within aglove, or included in a handheld device, for example, that allows a userto place a finger into the device 300 for measurement of the user's BP.The illustrated embodiment of the device 300 includes an immobilizer302, a substrate 308, and a TSA 310. The other features of devices 100and/or 200 that are not shown in FIG. 3 may also be included, but havebeen omitted for sake of brevity.

The immobilizer 302, which may be a cuff that does not fully wrap arounda user's finger, may be mounted to stable surface, such as a desk,counter, sink, included in a finger of a glove, or part of a handhelddevice. The substrate 308 and the TSA 310 may be mounted on an innersurface of the immobilizer 302. In some embodiments, at least the TSA310 may be mounted offset from a bottom of the immobilizer 302 so thatit may be aligned to a digital artery, such as the ulnar artery.

In operation, a user may place a finger into the device 400 so that theTSA 310 is aligned correctly. The immobilizer 302 may include markingsto inform the user the desired finger placement to achieve the desiredarterial alignment. Upon pressing onto the device 400, the TSA 310 maybegin to measure capacitive changes in the TSA 310 to estimate digitalBP of the user. In some embodiments, the device 400 may include one ormore indicators (not shown), such as LEDs, to indicate to the user ifenough pressure is being applied, whether correct alignment has beenobtained, and when the reading is complete.

FIG. 4 is a functional block diagram of a finger-wearable BP monitoringdevice 400 in accordance with an embodiment of the present disclosure.The device 400 may be an example of the devices 100, 200, and/or 300. Inthe depicted embodiment, device 400 includes control circuitry 412. Thecontrol circuitry 412 may be one implementation of the control circuitry112, 212 and/or 312. The illustrated embodiment of the control circuitry412 includes a power supply 405 and a controller 415. The illustratedembodiment of power supply 405 includes an energy harvesting antenna407, charging circuitry 409, and a battery 411. The illustratedembodiment of controller 415 includes control logic 417, BP logic 419,ADC 447, multiplexer 449, and communication logic 421.

Power supply 405 supplies operating voltages to the controller 415 andvarious other sensors and components of the device 400. Antenna 423 isoperated by the controller 415 to communicate information to and/or fromdevice 400. In the illustrated embodiment, antenna 423, controller 415,and power supply 405 are disposed on substrate, such as the substrate108.

In the illustrated embodiment, power supply 405 includes a battery 411to power the various embedded electronics, including controller 415.Battery 411 may be inductively charged by charging circuitry 409 andenergy harvesting antenna 407. In one embodiment, antenna 423 and energyharvesting antenna 407 are independent antennae, which serve theirrespective functions of energy harvesting and communications. In anotherembodiment, energy harvesting antenna 407 and antenna 423 are the samephysical antenna that are time shared for their respective functions ofinductive charging and wireless communications with reader 435. In yetother embodiments, the battery 411 may be charged via a wire pluggedinto the device 400.

Charging circuitry 409 may include a rectifier/regulator to conditionthe captured energy for charging battery 411 or directly powercontroller 415 without battery 411. Charging circuitry 409 may alsoinclude one or more energy storage devices to mitigate high frequencyvariations in energy harvesting antenna 407. For example, one or moreenergy storage devices (e.g., a capacitor, an inductor, etc.) can beconnected to function as a low-pass filter.

Controller 415 contains logic to choreograph the operation of the otherembedded components. Control logic 417 controls the general operation ofdevice 400, including providing a logical user interface, power controlfunctionality, etc. Additionally, control logic 417 controls theinflation and deflation of the bladder 406 and receives pressure datafrom a pressure sensor included in the bladder 406. Analog to digitalconverter (ADC) 447 may receive data from the other sensors 425 and thesensor array 410. The ADC 447 may convert the received data to a digitalformat and provide the same to the control logic 417 and/or the BP logic419. In some embodiments, the ADC 447 may be coupled to the sensor array410 and the other sensors 425 via the MUX 449, which controls the inflowof data to the ADC 447.

The BP logic 419 may receive the capacitance measurements form thesensor array 410 and convert the capacitance measurements intoequivalent pressure values. The pressure values may be in mmHg, forexample. The pressure values may further be converted into pressurewaves that may be analyzed in either the time or frequency domains todetermine MAP, SBP and DBP at the digital artery. In some embodiments,the blood pressure data at the digital artery may be transformed tocorresponding blood pressure data at the brachial location, for example.The pulse waves may be analyzed by the BP logic 419 to determine apressure at which a maximum pulsatile amplitude occurs. The determinedpressure may be based on one capacitive sensor of the sensor array 410,on an average of all the capacitive sensors, or based on a lowestdetermined pressure.

In some embodiments, the BP logic 419 may receive sound recordings froma microphone to implement auscultatory blood pressure estimation. Themicrophone may be part of the other sensors 425, which may be arrangedto record blood pulses occurring in the digital artery. The BP logic 419may analyze the sound recordings in relation to pressure data receivedfrom the bladder 406 (due to a pressure sensor in the bladder 406) todetermine a pressure when Korotkoff sounds begin and end. If thepressure in the bladder 406 is decreasing during this time, the pressurecorresponding to the beginning of the Korotkoff sounds may be anestimate of the SBP, whereas the pressure corresponding to the ending ofthe Korotkoff sounds may be an estimate of the DBP.

In some embodiments, the BP logic 419 may determine the MAP, SBP and DBPusing oscillometry. The determination of the MAP, SBP and DBP may besimilar to the applanation tonometry techniques but the pressure sensormeasurements may be used instead of the capacitive measurements of theTSA 410. For example, the pressure sensor included in the bladder 406may measure pressure changes due to blood flow in the digital arterypressing the finger on the bladder 406. The pressure corresponding towhen a maximum amplitude of a pressure pulse may be an estimate of theMAP. Subsequently, the BP logic 419 may determine the SBP and DBPthrough one or more regressions.

In some embodiments, the BP logic 419 may perform BP estimations usingall three techniques. The BP estimations from the three differenttechniques may then be compared to determine a closest estimation of theuser's BP at the digital artery.

The control logic 417 may receive diagnostic data from the other sensors406, which may include a temperature sensor, accelerometer, PPG, andmicrophone. The data may be analyzed to determine if any of themeasurements are outside of established thresholds and, if so, responseaccordingly. For example, if accelerometer data shows that the fingerwas moving more than desired during a blood pressure reading, thecontrol logic 417 may reject that reading. Additionally, the controllogic 417 may determine the user's HR, RR, and/or SpO2 based on PPGsensor data. Lastly, temperature data may be used to adjust any bloodpressure estimations if the temperature is outside of an establishedrange.

Communication logic 421 provides communication protocols for wirelesscommunication with reader 435 via antenna 423. In one embodiment,communication logic 421 provides backscatter communication via antenna423 when in the presence of an electromagnetic field 451 output fromreader 435. In one embodiment, communication logic 421 operates as asmart wireless radio-frequency identification (“RFID”) tag thatmodulates the impedance of antenna 423 for backscatter wirelesscommunications. The various logic modules of controller 415 may beimplemented in software/firmware executed on a general purposemicroprocessor, in hardware (e.g., application specific integratedcircuit), or a combination of both.

The illustrated embodiment also includes reader 435 with a processor443, an antenna 445, and memory 437. Memory 437 includes data storage439 and program instructions 441. As shown reader 435 may be disposedoutside of device 400, but may be placed in its proximity to chargedevice 400, send instructions to device 400, and/or extract data fromdevice 400. In one embodiment, reader 435 may resemble a hand heldportable device that provides a holder or case for the device 400.

External reader 435 includes the antenna 445 (or group of more than oneantennae) to send and receive wireless signals 451 to and from device400. External reader 435 also includes a computing system with theprocessor 443 in communication with the memory 437. Memory 437 is anon-transitory computer-readable medium that can include, withoutlimitation, magnetic disks, optical disks, organic memory, and/or anyother volatile (e.g., RAM) or non-volatile (e.g., ROM) storage systemreadable by the processor 443. Memory 437 can include a data storage 439to store indications of data, such as data logs (e.g., user logs),program settings (e.g., to adjust behavior of device 400 and/or externalreader 435), etc. Memory 437 can also include program instructions 441for execution by processor 443 to cause the external reader 435 toperform processes specified by the instructions 441. For example,program instructions 441 can cause external reader 435 to provide a userinterface that allows for retrieving information communicated fromdevice 400 or allows transmitting information to device 400 to programor otherwise select operational modes of device 400. External reader 435can also include one or more hardware components for operating antenna445 to send and receive wireless signals 451 to and from device 400.

External reader 435 can be a smart phone, digital assistant, or otherportable computing device with wireless connectivity sufficient toprovide the wireless communication link 451. External reader 435 canalso be implemented as an antenna module that can be plugged into aportable computing device, such as in an embodiment where thecommunication link 451 operates at carrier frequencies not commonlyemployed in portable computing devices. In some embodiments, theexternal reader 435 may prompt a user of the device 400 to prepare for aBP reading, which may provide the user a moment to position the fingerat an elevation equal with their heart. Additionally, while the BPreading is being performed, the external reader 435 may provide adistraction to the user. For example, the distraction could take theform of a news article, current weather conditions, a game, or displayheart beat waveforms and BP measurements.

FIG. 5 is a plan view of a tactile sensor array 510 in accordance withan embodiment of the present disclosure. The tactile sensor array (TSA)510 may be an example of the TSAs 110, 210, 310, and/or 410. Theillustrated embodiment of TSA 510 may include a plurality of capacitivesensors 528 arranged into an array having columns 530 and rows 532. Insome embodiments, a substrate 508 may provide mechanical support for theTSA 510, and may be mounted or disposed on an inner surface 516 of acuff 502. In some embodiments, the TSA 510 may have asemi-circumferential shape to for or fit around at least a portion of afinger, and or to an inner surface of a cuff, such as the cuff 102. Inother embodiments, the TSA 510 may be flexible so that it can conform tothe finger.

Each capacitive sensor 528 may be formed from a metal-insulator-metalcapacitor, with the insulator capable of being deformed in the presenceof pressure. Due to the deformation, e.g., flattening, of the insulator,the capacitance of the individual capacitive sensor 528 may change. Forexample, if a capacitive sensor 528 flattens, then the distance betweenthe two conductors decreases, which increases the capacitance of thesensor 528. On the other hand, if the capacitive sensor 528 is stretchedso that the distance between the two conductors increases, then thecapacitance decreases. Additionally, if a capacitive sensor 528 is bent,the edges of conductors that form the two electrodes may move closertogether, which may also affect the capacitance. By measuring the amountof change of the capacitance, increase in capacitance for example, anindicative amount of pressure being applied to the capacitive sensor 528may be determined.

In some embodiments, the columns 530 may be arranged to be parallel witha digital artery. In such an embodiment, several instances of thecapacitive sensors 528 in a same column may be aligned with the digitalartery. In some embodiments, the number of columns may be greater thanthe number of rows to ensure that the TSA 510 overlays the desireddigital artery when a finger-wearable device is worn by a user. WhileFIG. 5 shows 7 columns and 6 rows, other numbers of columns and rows maybe implemented, such as 10 columns and three rows. Additionally, thepitch between adjacent columns 530 may be such that the distance betweenthe columns may provide for a single column to overly the digitalartery. For example, the pitch between columns 530 may be 0.75 mm insome embodiments. However, due to inexact alignment of the TSA 510 witha digital artery, instances of use may have multiple columns 530 atleast partially overlapping the digital artery.

FIGS. 6A and 6B are a cross-sectional view and a plan view,respectively, of a TSA 610 in accordance with an embodiment of thepresent disclosure. TSA 610 may be an example of the TSA 110, 210, 310,410 and/or 510. The TSA 610 includes a plurality of capacitive sensors628 that form an array. The array of capacitive sensors 628 may bearranged into a grid having rows and columns. The illustrated embodimentof the TSA 610 includes a plurality of layers that combine to form eachof the plurality of capacitive sensors 628, see FIG. 6A. The pluralityof layers includes a support layer 646, a first electrode layer 644, andielectric pillar layer 642, a second electrode layer 640, a protectivelayer 638, and a shield layer 636. The support layer 646 may providemechanical support to the various other layers of the TSA 610.Additionally, the support layer 646 may be disposed on a substrate, suchas the substrate 108, when the TSA 610 is mounted in a finger wearablecuff. On the other side of the TSA 610, the shield layer 636 may befinger facing, and may provide some protection of the internal layers ofthe TSA 610 from the finger. Additionally, the shield layer 636 mayreduce parasitic capacitance formed between the finger and the first andsecond electrodes layers 644 and 640.

The first electrode layer 644 may form one side of ametal-insulator-metal (MIM) capacitor, which form each of the capacitivesensors 628. In some embodiments, the first electrode 644 may bepixelated for each of the plurality of capacitive sensors 628. The firstelectrode 644 may be formed from a conductive material, such as a metalor conductive polymer. Additionally, each electrode in the firstelectrode layer 644 may be individually coupled to traces that providerespective outputs for the capacitive sensors 628.

The second electrode layer 640 may be the second conductive layer in theMIM capacitor that forms the capacitive sensors 628. The secondelectrode layer 628 may be formed from the same or similar materials asthe first electrode layer 644. While not shown, the second electrodelayer 640 for each capacitive sensor 628 may be coupled to a conductivetrace that provides an electric coupling to each capacitive sensor 628so that the capacitance of each capacitive sensor 628 may beindividually measured.

The dielectric pillar layer 642 may include a plurality of separate andindividual pillars formed into an array, and which may form theinsulator layer in the MIM capacitor. While the dielectric pillar layer642 is shown to be formed from individual pillars, the layer 642 mayalso be formed from a continuous layer of soft material with thepixelated first and second electrode layers 640 and 644 formed onopposing sides. Each of the individual pillars may be disposed betweenthe first and second electrode layers 644 and 640. Additionally, each ofthe individual pillars may be deformable so that they are able todecrease in height due to pressure, or even extend in height if pulled.The deformation of the individual pillars may change the capacitance ofeach of plurality of dielectric pillars. Additionally, the first andsecond electrode layers 640 and 644 may deform in gaps between adjacentcapacitive sensors 628, where the deformation may also affect thecapacitance of the sensor. The change in capacitance may be provided asa capacitance level signal in some embodiments, which may be indicativeof the amount of pressure being applied. In some embodiments, eachpillar of the dielectric pillar layer 642 may be formed from a soft,flexible dielectric material, such as silicone for example.

The protective layer 638 may be disposed over the second electrode layer640, and may provide some mechanical support and protection to the TSA610. In some embodiments, the protective layer 638 may provide supportto the electrical traces coupled to the second conductive layer 640 ofeach capacitive sensor 628. In some embodiments, the protective layer638 may be formed from Kapton.

In some embodiments, the protective layer 638 may have slits 648 formedtherein between adjacent capacitive sensors 628. In some embodiments,the slits 648 may be formed only in the column direction, e.g., alignedwith the finger, to mechanically decoupled adjacent columns. Bymechanically decoupling adjacent columns, the capacitive sensors 628 inthe adjacent columns may be more sensitive to pressure changes in thedigital artery. In some embodiments, the slits 648 may be formed in boththe column and row directions, thereby mechanically decoupling thecapacitive sensors 628 in both directions. Forming the slits 648 in bothdirections may provide additional mechanically decoupling and increasessensitivity to the capacitive sensors 628.

The plan view of TSA 610 shown in FIG. 6B shows the support layer 646,individual areas of the first electrode layer 640/644, individualdielectric pillars of the dielectric pillar layer 642, and theprotective layer 638. The protective layer 638 is depicted by thetransparent cross-hatching that covers the entirety of FIG. 6B. Slits648 are shown to be formed between individual ones of the capacitivesensors 628 in both column and row directions, but some embodiments mayonly include slits 648 in one of the directions.

FIGS. 7A and 7B are a cross-sectional view and a plan view,respectively, of a TSA 710 in accordance with an embodiment of thepresent disclosure. The TSA 710 may be an example of the TSA 110, 210,310, 410 and/or 510. The TSA 710 includes a plurality of capacitivesensors 728 arranged in a two-dimensional array. The two-dimensionalarray may be arranged in columns and rows, similar to the TSA 510, withthe number of columns outnumbering the number of rows. The columns maybe aligned longitudinally with a finger whereas the rows may be alignedcircumferentially with the finger.

The illustrated embodiment of the TSA 710 includes a support layer 746,a first electrode layer 744, a dielectric pillar layer 742, a secondelectrode layer 750, and a protective layer 752. The support layer 746,first electrode layer 744, and dielectric pillar layer 742 may besimilar to like layers of the TSA 610, and, as such, will not bediscussed in detail for sake of brevity. The combined layers of the TSA710 may form the plurality of capacitive sensors 720, which may be MIMcapacitors formed from the first and second electrode layers disposed onopposite sides of a dielectric pillar of the dielectric pillar layer742. Due to the deformable nature of the dielectric pillars, thecapacitance of each of capacitive sensor 728 may change when thepressure or tension is applied to the capacitive sensors 728 of the TSA710.

The second electrode layer 750 may be formed form a conductive cloththat extends across the TSA 710. The conductive cloth may provide theconductor for one side of the capacitive sensors 728 along withelectrical traces from each capacitive sensor to receive data signals.The use of the conductive cloth may allow each capacitive sensor 728freedom to move without the movement being transferred to an adjacentcapacitive sensor.

The protective layer 752 may be a continuous layer disposed on thesecond electrode layer 750. The protective layer 752, which may befinger facing, may provide physical protection from interaction with thesurrounding environment. In some embodiments, the protective layer 752may be soft and flexible so not to restrict movement, e.g., compression,of the underlying dielectric pillar layer 742. For example, theprotective layer 752 may be formed from silicone, polyurethane film, orother soft, flexible plastic.

The plan view of TSA 710 shown in FIG. 7B shows the support layer 746,individual areas of the first electrode layer 744, individual dielectricpillars of the dielectric layer 742, and the second electrode 750. Thesecond electrode 750 is depicted by the transparent cross-hatching thatcovers the entirety of FIG. 7B.

FIG. 8 is a bladder 806 in accordance with an embodiment of the presentdisclosure. The bladder 806 may be an example of the bladders 106, 206,and/or 406. The bladder 806 may be disposed on an inner surface 816 of acuff 802. The illustrated embodiment of the bladder 806 may be coupledto an air pump 854 and a pressure sensor 856 may be disposed within thebladder 806. In some embodiments, the air pump 854 may pump air into thebladder 806 in response to a control signal from control circuitry 112,for example. The pressure sensor 856 may measure the pressure of thebladder 806, which may be provided to the control circuitry 112 inresponse. Additionally, the air pump 854 may deflate the bladder 806 ata desired controlled rate, also in response to a control signal from thecontrol circuitry 112.

The bladder 806 may be formed from a flexible, stretchable material sothat it inflates in response to introduction of air. For example, thebladder may be formed form a soft, stretchable plastic, polyurethane, orlatex. In response to deflation, the bladder 806 may retake a taut formacross the inner surface 816 so not to interfere with removal of thecuff 802 from a finger, or from inserting the finger into the cuff 806.In some embodiments, the bladder 806 may, in relation to the size of thefinger, have a length that is 80% and a width that is 40% of acircumference of a finger. In other embodiments, the bladder 806 may bedisposed on an inner surface of the cuff 802 on an opposite side from aTSA. The pressure sensor 856 may be disposed on the inner surface of thecuff 802 within the bladder 806. In some embodiments, the pressuresensor 856 may be a MEMS-type pressure sensor.

In operation, the air pump 854 may pump air into the bladder 806 inresponse to the control signal, and the pressure sensor 856 may monitorthe internal pressure of the bladder 806. The internal pressuremeasurements may be provided to the control circuitry to determine whento cease inflation.

FIG. 9 is a bladder 906 in accordance with an embodiment of the presentdisclosure. The bladder 906 may be an example of the bladder 106, 206and/or 406. The illustrated embodiment of the bladder 906 includes aheating coil 958, a refrigerant 960, and pressure sensor 956. Theheating coil 958 may be disposed on an inner surface 916 of a cuff 902,and arranged within the bladder 906. The bladder 906 also being disposedon the inner surface of the cuff 902. To inflate the bladder 906, therefrigerant may undergo a phase transition from a liquid to a gaseousstate.

The bladder 906 may be formed from similar materials as the bladder 806.However, the bladder 906 may be formed from materials that will notreact with or be degraded by the refrigerant 960. In some embodiments,an inner surface of the bladder 906 may be coated with a non-reactivematerial to avoid degradation due to the refrigerant 960.

The refrigerant 960 may be in a liquid phase in a default state, but mayundergo a phase transition to a gas phase when heated. The transition tothe gas phase may inflate the bladder 906. The refrigerant may be a highboiling point refrigerant that may be converted to the gas phase at atemperature above body temperature, for example. For example, therefrigerant may be R-113 refrigerant, which is trichlorotrifluoroethane,that has a boiling point around 50° C.

In some embodiments, the heating coil 958 may be coupled to receivepower from the control circuitry 112, for example. Providing power tothe heating coil 958 may heat the refrigerant 960 to cause a phasechange. The heating coil 958 may be formed from a metallic conductorthat will not react with the refrigerant 960, or may be coated with anon-reactive material. Control circuitry 112 may provide the power tothe heating coil 958 to heat the refrigerant 960 to at least its boilingpoint. Boiling the refrigerant will provide the needed gas to inflatethe bladder 906.

The pressure sensor 956, which may be similar to the pressure sensor856, may monitor the internal pressure of the bladder 906 and providepressure data to control circuitry 112 in response. The controlcircuitry 112 may determine when to remove power from the heating coil958 to deflate the bladder 906.

FIG. 10 is a bladder 1006 in accordance with an embodiment of thepresent disclosure. Bladder 1006 may be an example of the bladder 106,206, 406 and/or 906. The bladder 1006 may be similar to the bladder 906except that the refrigerant 1060 and heating coil 1058 may be disposedwithin a reservoir 1062 instead of within the bladder 1006. Thereservoir 1062 may be fluidically coupled to the bladder 1006 via aconduit/channel 1064. Refrigerant 1060 may be in a liquid state in thereservoir 1062. When the heating coil 1058 receives power, therefrigerant 1060 within the reservoir 1062 may undergo the phase changeto the gas phase, then move through the conduit 1064 into the bladder1006 to inflate the bladder. While only one reservoir 1062 is shown, andis located at one end of the bladder 1006, in other embodiments, asecond reservoir 1062 may be coupled to an opposite end of the bladder1006. In such a configuration, the refrigerant 1060 may flow back intoone of two reservoirs after returning to the liquid phase.

FIG. 11 is an example pressure plot 1100 in accordance with anembodiment of the present disclosure. The plot 1100 shows the relationof pressure and time when a finger-wearable blood pressure monitoringdevice, such as the device 100, performs a blood pressure readingoperation. The plot 1100 will be used to further discuss the operationof the device 100, for example. While the plot 1100 may be described inrelation to the device 100, the plot 1100 may also be used to illustratethe operation of the other embodiments discussed herein.

The plot 1100 shows the capacitance readings from all of the capacitivesensors from a TSA 110 in units of mmHg plotted against time. Forexample, the plot 1100 may show the capacitance readings of 30individual capacitive sensors. Each pressure wave extracted from thecapacitive measurements includes pulsatile components that occur whenthe pressure applied to the digital artery due to the TSA 110 beingpressed against it is similar to the internal pressure in the digitalartery, e.g., the blood pressure. The capacitance values from the TSA110 may be converted to pressure due to the direct influence thepressure has on the capacitance sensors.

At time t0, the bladder 106 may be in a deflated state so that no orlittle pressure may be applied to the TSA 110 by a finger. At time t1,the bladder 106 may be inflated in response to one or more controlsignals from the control circuitry 112. The bladder 106 may be inflatedto a pressure that is at least greater than a systolic BP of the user.The black dashed line shows the pressure in the bladder 106 as recordedby a pressure sensor, such as the pressure sensor 856. As the pressurereaches a desired maximum at t2, the control circuitry 112 may cause thepressure of the bladder 106 to decrease at a slow, controlled rate. Forexample, the bladder 106 may deflate at 2-3 mmHg/second. While the plot1100 shows the pressure at time t2 to be around 200 mmHg and higher,which is above typical SBP readings, the maximum pressure may be lessthan 200 mmHg depending on the user's average SBP. However, in someembodiments, the bladder 106 may be inflated until occlusion of thedigital artery is obtained.

Between times t1 and t2, the bladder 106 presses the finger onto the TSA110 to cause the TSA 110 to deform a digital artery. For example, theTSA 110 may be pressed onto the skin and tissue that is directly overthe digital artery. Pressing the TSA 110 firmly into the tissue over thedigital artery may cause one or more columns of capacitive sensors to bepressed onto the tissue directly over the digital artery, for example.It may be desirable that the size of the capacitive sensors is such thata single capacitive sensor, or a column of sensors, is smaller than thediameter of the digital artery. A pitch between the columns may be lessthan the diameter of the digital artery as well. Sizing the capacitivesensors as such may assist with applanation tonometry. In general, itmay be desirable to have at least one capacitive sensor centered on thedigital artery.

As the pressure reaches a maximum at t2, the digital artery may bedeformed to affect the blood flow within the digital artery. However, asthe bladder 106 deflates, the pressure in the digital artery decreasesaccordingly. Additionally, the arterial wall being pressed on by the TSA110 may begin to revert back to a normal condition, e.g., unobstructed.However, as the arterial wall gets close to its unobstructed condition,the arterial wall passes through a condition where it appears infinitelyflat in regards to the size of the capacitive sensors pressing on it,e.g., the local radius of curvature approaches infinity. At this point,the transmural pressure may be zero. The transmural pressure being thedifference between the internal pressure and the external pressure. Theinternal pressure would be the blood pressure, and as such the equalexternal pressure may provide a measurement of the blood pressure. Whenthe local radius of curvature reaches this condition, the arterial wallmay provide maximum pulsatile pressure due to blood flowing in responseto heart beats. However, as the arterial wall moves through this state,the pulsatile pressure will begin to increase then decrease as shown bythe increase in pulsatile pressures between t3 and t4, and thesubsequent decrease in pulsatile pressures between t4 and t5.

At time t3, the arterial wall begins to near the local radiusapproaching infinity condition, at this time pulsatile pressure maybegin to be measured by the TSA 110. The measured pulsatile pressures,which are due to the blood flow in response to heart beats, may begin toincrease until time t4 due to the changing shape of the arterial wall.At time t4, the arterial wall may reach maximum flatness, e.g., thecurvature with respect to a capacitive sensor approaches infinity, whichprovides the pulsatile pressure with the maximum amplitude. Further,between times t4 and t5 the pulsatile pressure will decrease until nopressure is applied by the bladder 106.

The applied pressure corresponding to the maximum pulsatile amplitudemeasured at time t4 may represent, or be an estimation of, the meanarterial pressure (MAP) at the digital artery. In some embodiments, theMAP estimation may be based on the capacitance changes of a singlecapacitive sensor, or a column of capacitive sensors. In otherembodiments, the MAP estimation may be based on an average of all thecapacitive sensors of the TSA 110. In yet another embodiment, the MAPestimation may be based on the capacitive sensor providing the lowestpressure reading. As noted in plot 1100, the MAP estimate is estimatedto be 79 mmHg, whereas the reference MAP is 82 mmHg. The reference MAPmay be a user's MAP based on a brachial BP measurement, for example, orbased on standard BP guidelines.

Additionally or alternatively, auscultation may be used to estimate theblood pressure in the digital artery. To implement the auscultation, themicrophone 226 may be used to record the sound of the blood pulsesoccurring in the digital artery. To perform blood pressure monitoringusing the auscultation principles, the bladder 106 may be inflated toobtain occlusion of the digital artery. After the digital artery isoccluded, the bladder 106 may be decreased in pressure at a slow andcontrolled rate. As the pressure decreases, the blood begins to flow inthe digital artery causing audible pulses that may be recorded by themicrophone 226. These pulses may be referred to as Korotkoff sounds.Pressures corresponding to the start and end of the Korotkoff sounds mayestimate the SBP and DBP, respectively, of the user. The auscultatorytechnique may be implemented in addition to or as an alternative to theapplanation tonometry technique.

Further, oscillometry may be implemented to estimate MAP, SBP and DBP atthe digital artery based on the pulses in the blood flow that occurduring the decrease in pressure by the TSA 110 in the digital artery.For example, pressure readings from a pressure of the bladder 106 maymeasure pressure pulses occurring due to the blood flow. The pressurepulses may show similar pressure measurements as shown in the plot 100.The pressure pulse with the maximum amplitude may be an estimate of theMAP, which may be used to estimate SBP and DBP.

FIG. 12 is a method 1200 in accordance with an embodiment of the presentdisclosure. The method 1200 may be an example operation of the device100, 200, and/or 300. The method 1200 outlines some of the steps indetermining at least the digital blood pressure of a user using afinger-wearable blood pressure monitoring device. In some embodiments,the device may implement applanation tonometry to determine the bloodpressure. In other embodiments, oscillometry or auscultation may beimplemented in addition to or instead of the applanation tonometry.While the method 1200 is discussed in terms of slowly deflating thebladder to determine the BP at the digital artery, the method 1200 mayalso be used during a slow, controlled inflation of the bladder.

The method may begin at step 1202 with inflating a bladder of a fingerwearable blood pressure monitoring device to a first pressure. Inflatingthe bladder may cause a finger of a user to be pressed into a TSA of thedevice. In some embodiments, the first pressure may be a pressure atleast greater than a SBP of the user. In other embodiments, the firstpressure may be high enough to occlude blood flow in a digital artery ofthe finger.

The step 1202 may be followed by step 1204, which includes deflating thebladder at a controlled rate once reaching the first pressure. In someembodiments, the bladder may be deflated at a rate of 2 to 3 mmHg/s. Thestep 1204 may be followed by step 1206, which includes while deflatingthe bladder, monitoring capacitance level changes of one or morecapacitive sensors of the tactile sensor array, wherein the capacitancelevel changes are indicative of pressure changes within a digital arteryof the finger. While inflating the bladder may press the TSA into thefinger so that the underlying digital artery is deformed or occluded,deflating the bladder in a controlled manner may allow for the changesin pressure internal to the digital artery due to the physicaldeformation of the artery in addition to the blood pressure to bemeasured.

The step 1206 may be followed by the step 1208, which includes based onthe monitoring, determining a maximum pulse amplitude of the blood flowin the digital artery based on the capacitance level changes. Themaximum pulse amplitude may be determined from the maximum capacitancechanges measured by the TSA in response to the blood flow in the digitalartery. The maximum capacitance changes may be measured when the localradius of curvature of the digital artery approaches infinity, whichallows the arterial wall to move a maximum distance in response to theblood pressure.

The step 1208 may be followed by the step 1210, which includesestimating a mean arterial pressure in the digital artery based on themaximum pulse amplitude. The mean arterial pressure may be estimatedfrom the applied pressure where the maximum pulse amplitude occurs. Insome embodiments, the applied pressure where the maximum pulse amplitudeoccurs may be an average of all capacitive sensors of the TSA, or may bebased on a lowest pressure recorded by the TSA. In some embodiments, thepulsatile waves measured by the TSA may be analyzed in the frequencydomain to determine the mean arterial pressure.

Any of the steps 1202-1210 may be followed by optional steps 1212through 1218, which include the measurement of other diagnosticvariables. Additionally, the steps 1212-1218 may be performed in anyorder and/or in isolation of any of the other steps. For example, step1212 may include determining a systolic and diastolic blood pressurebased on the mean arterial pressure. Optional step 1214 may be performedas well, and includes determining a temperature of the finger using atemperature sensor and adjusting the estimate of the mean arterialpressure if the temperature is outside of a temperature range.Additionally, optional step 1216 may be performed, which includesdetermining movement of the finger using an accelerometer and rejectingthe estimation of the mean arterial pressure if the movement is outsideof a movement threshold. Further, step 1218 may be performed, whichincludes determining a heart rate, a respiratory rate, and an oxygensaturation of the user using a PPG sensor of the finger wearable bloodpressure monitoring device.

In addition to the process steps listed above, various other steps maybe performed, such as transmitting the blood pressure data and otherdata to an external reader for displaying to the user and/or providingto a physician. In some embodiments, the data may be provided to thephysician through an associated application or via the user's electronicmedical records.

The order in which some or all of the process blocks appear in process1200 should not be deemed limiting. Rather, one of ordinary skill in theart having the benefit of the present disclosure will understand thatsome of the process blocks may be executed in a variety of orders notillustrated, or even in parallel.

The processes explained above are described in terms of computersoftware and hardware. The techniques described may constitutemachine-executable instructions embodied within a tangible ornon-transitory machine (e.g., computer) readable storage medium, thatwhen executed by a machine will cause the machine to perform theoperations described. Additionally, the processes may be embodied withinhardware, such as an application specific integrated circuit (“ASIC”) orotherwise.

A tangible machine-readable storage medium includes any mechanism thatprovides (i.e., stores) information in a non-transitory form accessibleby a machine (e.g., a computer, network device, personal digitalassistant, manufacturing tool, any device with a set of one or moreprocessors, etc.). For example, a machine-readable storage mediumincludes recordable/non-recordable media (e.g., read only memory (ROM),random access memory (RAM), magnetic disk storage media, optical storagemedia, flash memory devices, etc.).

The above description of illustrated embodiments of the invention,including what is described in the Abstract, is not intended to beexhaustive or to limit the invention to the precise forms disclosed.While specific embodiments of, and examples for, the invention aredescribed herein for illustrative purposes, various modifications arepossible within the scope of the invention, as those skilled in therelevant art will recognize.

These modifications can be made to the invention in light of the abovedetailed description. The terms used in the following claims should notbe construed to limit the invention to the specific embodimentsdisclosed in the specification. Rather, the scope of the invention is tobe determined entirely by the following claims, which are to beconstrued in accordance with established doctrines of claiminterpretation.

What is claimed is:
 1. A finger-wearable blood pressure monitoringdevice, the device comprising: a cuff; a bladder disposed proximate tothe cuff; a pressure sensor coupled to the bladder to detect pressurechanges within a digital artery of a finger due to blood flow when thefinger wears the device, and wherein the bladder extends partially alonga circumference of an inner surface of the cuff and is disposed betweenthe pressure sensor and the finger when the finger wears the device; andcontrol circuitry coupled to the pressure sensor to receive pressuredata representative of the pressure changes and determine a bloodpressure based on the pressure data.
 2. The device of claim 1, whereinthe bladder is inflatable to cause the finger to be pressed onto thecuff when the bladder is inflated.
 3. The device of claim 2, wherein thebladder is coupled to a pump configured to pump air into the bladder toinflate the bladder.
 4. The device of claim 2, further including aheating element and a refrigerant disposed inside the bladder, whereinthe heating element is activated to cause the refrigerant to change froma liquid state to a gas state to inflate the bladder.
 5. The device ofclaim 2, further including a reservoir coupled to the bladder and aheating element disposed within the reservoir along with a refrigerant,wherein the heating element is activated to cause the refrigerant tochange from a liquid state to a gas state to inflate the bladder.
 6. Thedevice of claim 1, wherein a mean arterial pressure is determined basedon the pressure data.
 7. The device of claim 1, further comprising atactile sensor array positioned to additionally detect the pressurechanges based on changes to capacitance values, the tactile sensor arrayincluding a plurality of capacitive sensors formed from a plurality oflayers, the plurality of layers including: a first conductive layerdisposed on a substrate; a second conductive layer; deformabledielectric pillars disposed between the first and second conductivelayers, wherein each deformable dielectric pillar in combination withthe first and second conductive layers form an instance of a capacitivesensor of the tactile sensor array, and wherein a deformation of thedeformable dielectric pillars causes the capacitance values of thecapacitive sensor to change; a protective layer disposed on the secondconductive layer; and a shield layer disposed over the protective layer.8. The device of claim 7, wherein the protective layer is formed fromKapton, and wherein slits are formed in at least the protective layer toreduce mechanical coupling between instances of the plurality ofcapacitive sensors.
 9. The device of claim 1, further comprising atactile sensor array positioned to additionally detect the pressurechanges based on changes to capacitance values, the tactile sensor arrayincluding a plurality of capacitive sensors formed from a plurality oflayers, the plurality of layers including: a first conductive layerdisposed on a substrate; a second conductive layer; deformabledielectric pillars disposed between the first and second conductivelayers, wherein each deformable dielectric pillar in combination withthe first and second conductive layers form an instance of a capacitivesensor of the tactile sensor array, and wherein a deformation of thedeformable dielectric pillars causes the capacitance values of thecapacitive sensor to change; and a dielectric layer disposed on thesecond conductive layer.
 10. The device of claim 9, wherein the secondconductive layer is a continuous layer of conductive cloth.
 11. Thedevice of claim 1, wherein the cuff has a shape to fit at leastpartially around the finger, and wherein the cuff is adjustable to fitaround fingers of different sizes.
 12. The device of claim 1, furthercomprising a temperature sensor disposed proximate to the cuff todetermine a temperature of the finger when the cuff is worn by a user,and wherein the temperature sensor is further coupled to the controlcircuitry to provide the temperature to the control circuitry.
 13. Thedevice of claim 1, further comprising a microphone disposed proximate tothe cuff to record blood pulses in the digital artery, and wherein themicrophone is further coupled to the control circuitry to provide therecorded blood pulses to the control circuitry.
 14. The device of claim1, further comprising a photoplethysmography sensor disposed proximateto the cuff to emit light into the finger and measure an amount of lightexiting the finger when the finger wears the device, and wherein thephotoplethysmography sensor is further coupled to the control circuitryto provide the measurement of the amount of light exiting the finger tothe control circuitry.
 15. The device of claim 1, wherein the cuff andthe control circuitry are disposed inside a glove finger or mounted to astationary surface or a handheld device.
 16. A finger cuff bloodpressure measuring apparatus, the apparatus comprising: a cuff; abladder disposed proximate to the cuff; a pressure sensor coupled to thebladder to detect pressure changes within a digital artery of the fingerdue to blood flow when the finger is inserted in the cuff, and whereinthe bladder extends partially along a circumference of an inner surfaceof the cuff and is disposed between the pressure sensor and the fingerwhen the finger is inserted in the cuff; and control logic coupled tothe pressure sensor, the control logic including at least onemachine-accessible storage medium that provides instructions forobtaining a blood pressure estimation that, when executed by the controllogic, cause the apparatus to: determine, based on pressure datareceived from the pressure sensor, pressure changes due to blood flow inthe digital artery; and based on the pressure changes, determine a bloodpressure.
 17. The apparatus of claim 16, wherein the at least onemachine-accessible storage medium further provides instructions that,when executed by the control logic, cause the apparatus to; performfrequency domain analysis on the pressure data to determine a meanarterial pressure, a systolic blood pressure, and a diastolic bloodpressure at the digital artery.
 18. The apparatus of claim 16, wherein,the bladder is inflatable and positioned on the cuff to be pressedagainst the finger when the bladder is inflated, and wherein the atleast one machine-accessible storage medium further providesinstructions that, when executed by the control logic, further cause theapparatus to: inflate the bladder to a first pressure, the firstpressure at least greater than a systolic blood pressure of the user;upon reaching the first pressure, deflate the bladder at a controlledrate; and while the bladder is deflating, record pressure data from thepressure sensor to determine a maximum pulsatile due to blood flow inthe digital artery.
 19. The apparatus of claim 16, wherein the at leastone machine-accessible storage medium further provides instructionsthat, when executed by the control logic, further cause the apparatusto: determine a mean arterial pressure at the digital artery based onthe pressure data compare the mean arterial pressure to a threshold meanarterial pressure value; and provide an alert if the mean arterialpressure is above the threshold mean arterial pressure value, whereinthe alert is provided via an external reader.
 20. The apparatus of claim16, further comprising a temperature sensor disposed proximate to thecuff to determine a temperature of the finger, and wherein the at leastone machine-accessible storage medium further provides instructionsthat, when executed by the control logic, further cause the apparatusto: determine whether the temperature of the finger is below atemperature threshold; and instruct the user to warm up their finger ifthe temperature is determined to be below the temperature threshold.